The present invention relates generally to membrane type electrolytic cells for the production of chlorine, alkali metal hydroxides and hydrogen and more particularly to a cell which is adapted for experimental studies.
Chlorine and caustic are essential, large volume commodities used in all industrial societies. They are produced almost entirely electrolytically from aqueous solutions of alkali metal chlorides with the largest portion of such production coming from mercury and diaphragm cells. With the advent of technological advances such as dimensionally stable anodes, high activity catalytic cathodic materials and cation exchange, hydraulically impermeable permselective membranes, considerable improvements have been made in both product quality and energy efficiency. However, the complicated chemical structure of these membranes and their relative fragility make it difficult to optimize production parameters. For this, smaller cells are used to determine basic membrane characteristics, particularly their cationic and water transfer numbers and their dynamic properties under conditions typical of an operating cell, such as concentrated solution environments, elevated temperatures and high current densities must be used.
A rather extensive literature exists on the determination of ionic and water transport numbers for ion exchange membranes. For cationic transport both Hittorf-type electrolysis experiments and indirect emf methods have been used. In similar fashion, membrane water transport numbers can be measured by electrolysis techniques or by streaming potential techniques. Aside from the systematic discrepancies which have been observed between emf and the true electrolysis results, the former techniques do not lend themselves to studies using a high current density.
Electrolysis methods based on measuring changes in either electrolytic solution volume or weight are known. Volume methods are generally more convenient, but are susceptible to error due to membrane movement and are difficult to use at elevated temperatures. With this approach, even in carefully performed experiments, the best measurements at conditions of room temperature and low current density reported determinations of potassium ion transport numbers had an average relative standard deviation of 6%.
The need to create a measurable concentration change during electrolysis with this approach presents a further problem for cationic transport number measurements in concentrated solution environments. If concentration changes are kept small, it is difficult to obtain sufficient accuracy in solution analysis to obtain a reliable result. If larger concentration changes are produced, such membrane properties as water and electrolyte content are altered with the result that interpretation of the results become considerably more difficult.
It has been shown that the use of radiotracer techniques can be effective in largely removing the problem of concentration changes in the measurement of membrane transport parameters. These techniques, when applied in the improved test cell described herein, have led to a considerable improvement in the measurement of membrane characteristics under conditions typical of those used in production cells.